Power assisted steering for an automobile

Abstract

The invention relates to a power assisted steering system ( 21 ) that includes an electric assist motor ( 22 ) arranged to assist the manual force exerted by a driver on the steering wheel of the automobile, a processing means ( 23 ) arranged to control the electric assist motor ( 22 ), the processing means ( 23 ) including a means ( 28 ) for predetermining a signal (S 3 ) for controlling the electric assist motor on the basis of a first operation signal (S 1 ) determined on the basis of the angular position of the electric assist motor, and a second operation signal (S 2 ) determined on the basis of the measurement or calculation of the angular acceleration of the electric assist motor and the measurement or calculation of the assistance torque output by the electric assist motor.

The invention claimed is: 
     
       1. A power assisted steering system for an automobile comprising:
 an electric assist motor arranged to assist manual force exerted by a driver on a steering wheel of the automobile, 
 a processing means arranged to control the electric assist motor, 
 a means for calculating or measuring assist torque output by the electric assist motor, 
 a means for measuring angular position of the electric assist motor, wherein 
 the processing means comprises a means for determining a signal for controlling the electric assist motor on the basis of:
 a first operation signal determined on a basis of an angular position of the electric assist motor, 
 a second operation signal determined on a basis of:
 a measurement or calculation of angular acceleration of the electric assist motor, 
 a measurement or calculation of the assistance torque output by the electric assist motor. 
 
 
 
     
     
       2. The system according to  claim 1 , wherein the processing means comprises a means for comparing a theoretical dynamic state of the electric assist motor with an actual dynamic state of the electric assist motor determined from the measurement or calculation of the angular acceleration of the electric assist motor and the measurement or calculation of the assistance torque output by the electric assist motor, and wherein the processing means comprises a means for calculating the second operation signal arranged to calculate the second operation signal as a function of the comparison the theoretical and actual dynamic states of the electric assist motor. 
     
     
       3. The system according to  claim 2 , wherein the processing means comprises a first calculating means arranged to calculate, from the comparison of the theoretical dynamic state of the electric assist motor with the actual dynamic state of the electric assist motor, a signal representing a force resisting the steering rack. 
     
     
       4. The system according to  claim 2 , wherein the processing means comprises two calculating means arranged to calculate, from the comparison of the theoretical dynamic state of the electric assist motor with the actual dynamic state of the electric assist motor, a signal representative of the driver's action on the steering wheel of the automobile. 
     
     
       5. The system according to  claim 4 , wherein the means for calculating the second operation signal is arranged to calculate the second operation signal as a function of the signal representative of the force resisting the steering rack and the signal representative of the driver's action on the steering wheel of the automobile. 
     
     
       6. The system according to  claim 1 , wherein the means for determining the control signal of the electric assist motor is arranged to limit the taking into account of the second operation signal so as to keep the control signal in a defined interval on either side of the value of the first operation signal. 
     
     
       7. The system according to  claim 1 , further comprising a speed measuring means arranged to measure longitudinal speed of the automobile. 
     
     
       8. The system according to  claim 7 , wherein the processing means comprises a means for calculating the first operation signal arranged to calculate the first operation signal as a function of the angular position of the electric assist motor and the longitudinal speed of the automobile. 
     
     
       9. The system according to  claim 7 , wherein the means for calculating the second operation signal is arranged to calculate the second operation signal also as a function of the longitudinal speed of the automobile.